Cathode ray tube screen filming by a flow method



E. AT'JH EJW EM SCREEN FILMING BY A FLOW METHOD NW. N, 1956 CATHODE RAY TUBE 2 Sheets-Sheet 1 Filed Jan. 5, 1954 E. ATTI ,W 5 1 CATHODE RAY TUBE SCREEN FILMING BY A FLOW METHOD Filed Jan. 5, 1954 ELE 2 Sheets-Sheet 2 INVENTOR Eros AW.

ATTORNEY United rates Patent CATHUDE RAY THEE SCREEN FILMING BY A FLOW METHOD Eros Atti, Elmira, N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, PEL, a corporation of Pennsylvania Application January 5, 1954, Serial No. 402,207

21 Claims. (Cl. 117-335) This invention relates to the production of cathode ray tubes, and relates more particularly to the application of a lacquer film to the screen of a cathode ray tube prior to aluminizing, and to the drying of such a film.

For improving the performance of cathode ray tubes such as are used in television receivers, it is customary to provide aluminum backings for their phosphor screens. For most efficient reflection, the surface of the aluminum film in contact with the phosphor screen should be mirror smooth. Since the phosphor crystals present an irregular surface with large crevices between them unsuitable for the direct deposit thereon of an aluminum film, it is customary to place a transparent lacquer film on the phosphor for providing a smooth foundation layer upon which the aluminum film is deposited.

There are two known used methods for the filming of cathode ray tube screens. One, the flotation method, is accomplished by pouring a small amount of liquid filming lacquer on a water cushion inside the bulb of a tube which usually is dried after removal from the screening machine and then filled to a different depth with a fresh water cushion before filming. The lacquer preads over the whole cushion surface in the form of a thin sheet which is then deposited upon the screen during the pouring off of the water cushion, a tilt table or settling belt being used for decanting the water from beneath the lacquer film. This method is very critical, and the requirements for good filming are quite severe. The difficulties increase with the bulb size. The screens of some shapes of bulbs cannot be filmed by this method, in particular the screens of metal cone tubes.

The other method used is the spray method comprising the following steps. This method is mostly used for metal cone tubes. After being taken off the screening machine, the screen is dried in order to strengthen its bond to the faceplate. The screen is again wet with water to form the necessary water filling between the screen phosphor particles. The screen is then sprayed with the liquid filming lacquer while the bulb is rotated about a vertical axis with its faceplate upwards and the neck pointing downwards. The bulb is then centrifuged in this position for a few seconds to remove the excess lacquer. The bulb is then allowed to drain and dry in this position for a period of about twelve minutes. The film which covers the inner surface of the metal cone part of the bulb is then removed by trimming with a cutting wheel, and washing away with a water jet. The neck and funnel assembly is also cleaned off the film. Both liquid layers, lacquer film and water filling are then dried by air flow. Such a method is disclosed in Patent No. 2,644,770. The main disadvantages of such a method are the need for removing the unwanted film which covers the entire inner surface of a bulb; the complexities of spray gun maintenance; the difliculty of obtaining a film of uniform thickness and the need for a centrifuging and two drying operations.

My invention provides a flow filming method of filming the screens of cathode ray tubes which eliminates the difficulties discussed in the foregoing, of the flotation and spray filming methods. The screen is filmed by simply flowing by gravity over the surface of the wet screen when received directly from a screening machine, a small amount of liquid filming. lacquer which has been poured into the bulb. The bulb is rotated or rocked with the axis of its neck inclined at an angle to the vertical so that the lacquer is distributed over the entire screen surface by gravity. The desired film thickness is obtained by the drainage, by gravity, of the exces liquid. No centrifuging is required. The excess liquid is simply poured out or aspirated out of the bulb's neck after a small drainage interval, following which the double liquid layer is dried. In case that the excess lacquer has been poured out of the bulbs neck, a short water rinsing of the bulbs wall wet with filming lacquer--will remove all the unwanted filming lacquer from said bulbs wall.

Preferably the drying is accomplished as a feature of this invention, in two phases. In the first phase, air which is nearly saturated with water is blown into the bulb. Thi nearly saturated air slows down the evaporation of the water between the phosphor particles so that the lacquer film will not be disturbed by the passage of water vapor through it while the lacquer film 1.. still in the liquid phase. The rate of lacquer evaporation is high since the moist air acts completely dry for the lacquer evaporation. The screen water is then dried in the second phase by blowing a large volume of dry air into the bulb. This air may be warmed for further speeding-up the drying process. The water vapor passes easily through the now dry lacquer film which is many tens of times thinner than it was in the liquid state. Furthermore, the me chanical strength of the dry lacquer film is greatly increased compared to the strength of the liquid lacquer film so that for this additional reason it is not disturbed or ruptured by the passage through it of the evaporated water.

My improved lacquer filming method has many ad vantages over the flotation and spraying methods. One of the drying and one of the wetting steps is eliminated. The bulb size and shape do not present any serious limitation as with the flotation method. The filming process is less critical than in the flotation method. My filming method is simpler and more rapid than the spray method. Centrifuging is not required with my method, and consequently, l get a more uniform film which contains no concentric waves in the film or is the result of centrifuging. My method also eliminates the trimming and washing of unwanted film from the cone wall and neck-funnel assembly which are involved in the spray method. Furthermore, the freedom from unwanted film is better than that obtained by the spray method even after the trimming and washing of the unwanted film has been accomplished. My fiow filming met-bod provides r a much simpler, more rapid and cheaper method for automatic screen filming than can be accomplished by either the spray method or the flotation method. The amount of lacquer required is less than is require-d by the spray method.

My improved drying method provides a greatly reduced drying time without damage to the lacquer 'film. The drying can be accomplished in the same machine used for the filming. Intermediate handling of the bulbs being dried will not be required as formerly, and several advantages will be realized such as reduced time, less labor, and less shrinkage due to bulb mishandling since a transfer from a filming machine to a drying machine will not be necessary.

My improved screen filming method used with my improved film drying method in a single machine, thus results in greatly reduced cost and time, and in fewer rejects since a more uniform film is formed using my screen filming process, and less film damage results from the use of my film drying process.

An object of this invention is to improve the quality of lacquer films formed on the phosphor screens of cathode ray tubes prior to alumin-izing.

Another object of this invention is to reduce the cost of forming lacquer films on the phosphor screens of cathode ray tubes prior to aluminizing.

Another object of this invention is to reduce the time required for the formation of lacquer films on the phosphor screens of cathode ray tubes prior to aluminizing.

Another object of this invention is to reduce the time required for drying the lacquer films and underlying water layer formed on the screens of cathode ray tubes prior to aluminizing.

This invention will now be described with reference to the annexed drawings, of which:

Fig. l is a side elevation of a basic filming and drying machine with a bulb of a cathode ray tube clamped thereto, which may be used in the filming and drying processes of my invention;

Fig. 2 is a front elevation of Fig. 1;

Fig. 3 is a diagrammatic view showing the bulb in the loading and unloading position of the machine of Figs. 1 and 2;

Fig. 4 is a diagrammatic view showing the bulb in the lacquer dispensing position of the machine;

Fig. 5 is a diagrammatic View showing the bulb in the position for starting the flow of lacquer over the screen;

Fig. 6 is a diagrammatic view showing the bulb in the first draining position;

Fig. 7 is a diagrammatic view showing the bulb in the second draining position, and

Fig, 8 is a diagrammatic view showing the bulb in the third draining, water rinsing and drying position with drying equipment connected thereto.

Referring first to Figs. 1 and 2 of the drawings, the filming and drying machine has a base 10 having the two uprights 11 between which is rotatably supported the shaft 12. This shaft has the "spur gear 13 attached to one end thereof, and which is meshed with the worm gear 14 driven by the electric motor 15 which rotates the shaft 12 about its axis B. The electric motor 16 is supported from the shaft 12 by the metal cylinder 17 which extends around the rotary shaft 1-8 which is connected to 'the support 19 to which are pivoted the clamps 20 which clamp the bulb 21 in position. The motor 16 rotates the bulb assembly about the axis A of the neck of the bulb.

The motors 15 and '16 are conventional electric motors of the type having built-in speed reducing gearing and can be operated at different presettable speeds in order to accomplish the sequence of operations involved in the process.-

A bulb 21 to be filmed is unloaded from the conveyor of the settling room after the phosphor screen has been settled thereon, and is clamped between the clamps 20 while the machine is in the position shown by Fig. 3. The phosphor screen is still wet and excess water inside the bulb and on the screen is simply removed by draining.

The bulb will then be moved to the position shown by Fig. 4 where a small amount of lacquer will be introduced through the neck of the bulb and dispensed on the cone surfaces wall which will be the same side of the bulb where the surplus lacquer will later be drained out.

The bulb is then moved to the position shown by Fig. 5 with the axis A at about 55 from the vertical. Both motors 15 and 16 will now rotate. The motor 16 will rotate the bulb assembly about the axis A at about 10 R. P. M., while the motor 16 will rotate the bulb assembly about the axis B at about /3 R. P. M. The combined action of these two rotations will cause the lacquer to sweep the screens surface by describing a spiral path on this surface, starting at the screens edge and proceediug to the screens center which will be reached when the axis A is vertical with the faceplate downward. At this point, the motor 15 will be reversed to return the bulb to the position shown by Fig. 5, the lacquer sweeping for the second time the screens entire surface with the same continuous, gentle, spiral sweeping action, proceeding this time, from the screens center to its edge.

Rotation about the bulbs axis A will stop with the bulb in the position shown by Fig. 6, for about 15 seconds to allow the excess lacquer to drain from the cone rim.

The bulb will then be brought to the position shown by Fig. 7 where it will remain for about /2 minute to drain the excess lacquer from the screens surface.

The bulb is then moved to the position shown by Fig. 8 with the axis A vertical with the faceplate upwards and the excess lacquer is poured out. The bulb is left about one minute in this position to allow the excess lacquer to drain away from the bulbs area adjacent to the screen. Then the layer of unwanted liquid lacquer on the bulbs wall is removed by rinsing said unwanted liquid film from the bulb wall with water for a few seconds. A tube 30 having an outer diameter smaller than the inner diameter of the neck of the bulb is inserted in the bulb neck. Air is sent through the humidifier 32 which raises the relative humidity of the air to about, say or higher. The almost saturated airwhich must be within a certain temperature rangethen passes through the tube 30 against the screen of the bulb, this air passing out the neck of the bulb around the tube 30. This moist air drys the lacquer film quickly. The underlying water filling between the phosphor particles and under the lacquer film may be partially dried at a low rate of evaporation. The almost saturated air slows down the rate of evaporation of the water so that the lacquer film will not be damaged by the passage of water vapor through it. The rate of evaporation of the water may be brought to zero by using completely saturated air. This, however, is not necessary because the wet lacquer film has suificient strength to withstand a low water evaporation rate without damage.

Next, air of not too high relative humidity is passed through the heater 33, into the tube 30 to further dry the screen. The water evaporated by this dry warm air, passes easily through the dry lacquer film which is many tens of times thinner than when it was wet. Also, the strength of the dry film is much greater than when it was wet so that it withstands the passage of water vapor through it without damage.

During the first drying phase when the air is passed through the humidifier 32, the damper 34 at the inlet to the humidifier would be open, and the damper 35 at the inlet to the heater would be closed. In the second drying phase when dry air is blown into the bulb, the damper 34 would be closed and the damper 35 would be opened.

Another advantage of my flow filming process is that the thickness of the lacquer film is readily controlled. it is very important to have the correct thickness. Too thin films are permeable to the aluminum atoms so that instead of obtaining a smooth reflecting aluminum layer, sharply separated from the phosphor surface, a more or less pronounced volume aluminization of the phosphor particles near the screen surface is obtained with the result that the screen appears to be more or less gray. It can even appear black where the film is missing or excessively thin. A well aluminized screen has a brilliant light yellow color. Too thick films, on the other hand, may result in other troubles such as the films peeling off the screen or pulling the screen off the faceplate, or in cracks in the film with consequent blackening of the screen due to the diffusion of aluminum through the cracks.

In order to insure uniform screen brightness and color, the film thickness should not have excessive variations over the screen surface. Particularly objectionable are abrupt changes in film thickness because they are more readily detectable.

In my flow filming process, the film thickness and film distribution are exactly controlled by control of the flowing and draining conditions. Nocentrifuging is required. This fact together with the high speed of the flowing process has an important .influence upon the relation between the concentration of the filming lacquer and the thickness of the liquid film lacquer on the screen.

in 27" metal bulbs which have been successfully filmed using my process, a lacquer concentration (isobutyl methacrylate in toluene) has been used which is only 25% of the lacquer concentration used for spray filming. This less concentrated lacquer flows more readily, and the drainage time is reduced. By way of example, a 27" metal bulb filmed with a lacquer having a concentration of 40% with respect to the concentration used in the spraying method, required forty minutes for filming and draining. Reducing the concentration to 25% of that used for spray filming, resulted in reducing the filming and drainage time for the same sized bulb to only two minutes.

Using the 25 concentration means that the thickness of the liquid film at the beginning of the drying process must be about four times greater in bulbs filmed by my flow process than those filmed by the spray method for the conditions of equally thick dried films. This relatively thick liquid film possesses sufl'icient mobility in the direction parallel to the screen surface to cause irregularities in the thickness distribution of the film if the usual drying process is used. These irregularities may consist of local thickening of the film due to flowing of the lacquer on large areas of the screen under the influence of gravity, or in small areas of the screen due to excessively rapid evaporation of the water layer. Use of my improved drying process overcomes these difficulties.

A large variety of filming lacquer types may be used in my flow filming method because of the extreme simplicity of the process involved to film the screen--filming lacquers with isobutyl methacryla-te base for instance or nitrocellulose baseor of other different bases-may be used successfully. Excellent results have been obtained with a filming lacquer composed of isobutyl methacrylate or butyl methacrylate in toluene solution.

The mechanical action exerted upon the screen by my flow filming process is considerably weaker than that inherent in the spray filming process. The relatively weak bond between the phosphor screen and the faceplate possessed by the screen, as it comes off the settling machine, is capable of withstanding the flowing of the lacquer without any damage to the screen. Therefore, the practice required by the spraying or flotation process of first drying the screen to increase the strength of the phosphor bond to the faceplate, followed by a rewetting of the screen with water, can be abandoned with resulting saving of time and expense.

Following the drying process described in the foregoing, a bulb would be handled in the usual manner for aluminizing the screen and otherwise preparing it for duty as a cathode ray tube.

While it is preferred, for quantity production, that the bulbs be handled for screen filming and film drying in an automatic machine incorporating the principles illustrated by Figs. 1 and 2 of the drawings, other types of machines could be used, and the bulbs could be handled by hand for the practice of my screen filming and film drying methods.

r I claim as my invention:

1. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing a quantity of liquid lacquer within the bulb, tilting the bulb so that its faceplate is downwards and the axis of its neck is at an angle to the vertical,

and slowly rotating the bulb about the axis of its neck at a speed below that at which the centrifugal force would have an appreciable effect on said lacquer so that the lacquer flows in a spiral path over the surface of the screen.

2. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing a quantity of liquid lacquer within the bulb, tilting the bulb so that its faceplate is downwards and the axis of its neck is at an angle to the vertical, slowly rotating the bulb about the axis of its neck, and varying the angle of tilt at a slower rate while the bulb is rotated for causing the lacquer to flow in a spiral path over the surface of the screen.

3. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing a quantity of liquid lacquer within the bulb, tilting the bulb so that its faceplate is downwards and the axis of its neck is at an angle to the vertical, slowly rotating and tilting the bulb about the axis of its neck so that the lacquer flows in a spiral path over the surface of the screen, and stopping the rotation of the tube while maintaining the faceplate downwards and the axis of its neck at an angle to the vertical so that the excess lacquer flows by gravity from the screen.

4. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing liquid lacquer within the bulb, slowly rotating the bulb with its face plate downwards about the axis of its neck, with the axis of its neck at an angle to the vertical, and rotating the bulb about a horizontal axis extending through the axis of its neck at a slower angular rotation with respect to said rotation about the axis of said neck, the two rotations causing the lacquer to flow in a spiral path over the surface of the screen.

5. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing liquid lacquer within the bulb, tilting the bulb so that its face plate is downwards and the axis of its neck is at an angle to the vertical, slowly rotating and tilting the bulb about the axis of its neck so that the lacquer flows in a spiral path over the surface of the screen, and stopping the rotation of the bulb while maintaining the faceplate at an angle to the horizontal for draining the excess lacquer by gravity from the screen.

6. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, which comprises placing liquid lacquer within the bulb, flowing the lacquer by gravity over the surface of the screen, removing the excess lacquer from the bulb, drying the lacquer film by blowing a blast of relatively humid air within the bulb, and drying the water under the lacquer film by blowing a blast of relatively dry air into the bulb.

7. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, which comprises placing liquid lacquer within the bulb, flowing the lacquer by gravity over the surface of the screen, draining the excess lacquer by gravity from the screen, removing the excess lacquer from the bulb, drying the lacquer film by blowing a blast of relatively highly humid air within the bulb, and then drying the water under the lacquer film by blowing a blast of relatively dry air into the bulb.

8. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing liquid lacquer within the bulb, tilting the bulb so that its faceplate is downwards and the axis of its neck is at an angle to the vertical, rotating the bulb so that the lacquer flows in a spiral path over the surface of the screen, stopping the rotation of the bulb while maintaining the faceplate at an angle to the horizontal for draining the excess lacquer by gravity from the screen, removing the excess lacquer, drying the lacquer film by blowing relatively humid air into the bulb, and then drying the water under the lacquer film by blowing relatively dry air into the bulb. I

9. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a face plate and a neck portion, which comprises placing liquid lacquer within the bulb, tilting the bulb so that its faceplate is downwards and the axis of its neck is at an angle to the vertical, rotating the bulb about the axis of its neck so that the lacquer flows in a spiral path over the surface of the screen, stopping the rotation of the tube While maintaining the faceplate at an angle to the horizontal for draining the excess lacquer by gravity, removing the excess lacquer, drying the lacquer film by blowing relatively humid air into the bulb, and then drying the water under the lacquer film by blowing relatively dry air into the bulb.

10. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a faceplate and a neck portion, which comprises placing liquid lacquer Within the bulb, rotating the tube with its faceplate downwards about the axis of its neck, simultaneously rotating the bulb about a horizontal axis extending through the axis of its neck, the two rotations causing the lacquer to flow in a spiral path over the surface of the screen, stopping rotation of the bulb while maintaining the faceplate at an angle to the horizontal for draining the excess lacquer by gravity, removing the excess lacquer, drying the lacquer film by blowing relatively humid air within the bulb, and then drying the water under the lacquer film by blowing relatively dry air into the bulb.

11. The method of drying a phosphor screen of a bulb within a cathode ray tube, the screen having a wet lacquer film formed over a water film, which comprises blowing relatively humid air into the bulb to dry the lacquer film, and then blowing relatively dry air into the bulb for drying the water film.

12. The method of filming a water wetted phosphor screen within a bulb of a cathode ray tube with lacquer, said bulb having a faceplate and neck portion, which comprises placing liquid lacquer within the bulb, rotating the bulb about the axis of its neck while simultaneously rotating the bulb about a horizontal axis extending through the axis of its neck from a first position in which its faceplate is downwards with the axis of its neck at an angle to the vertical, to a second position in which its faceplate is downwards with the axis of its neck vertical, and from the second position back to the first position.

13. The method of filming a water wetted phosphor screen of a bulb of a cathode ray tube with lacquer, said bulb having a faceplate and a neck portion, which comprises placing a quantity of liquid lacquer within the bulb, slowly rotating the bulb about the axis of its neck while simultaneously rotating the bulb about a horizontal axis extending through the axis of its neck from a first position in which its faceplate is downwards with the axis of its neck at an angle to the vertical, to a second position in which its faceplate is downwards with the axis of its neck vertical, and from the second position back to the first position, stopping the rotation of the bulb atthe first position, and permitting the excess lacquer to drain by gravity from the surface of the screen.

l4. The method of filming a water wetted phosphor screen of a bulb of a cathode ray tube with lacquer, said bulb having a faceplate and a neck portion, which comprises placing liquid lacquer within the bulb, rotating the bulb about the axis of its neck while simultaneously rotating the bulb about a horizontal axis extending through the axis of its neck, from a first position in which its faceplate is downwards with the axis of its neck at an angle to the vertical, to a second position in which its faceplate is downwards with the axis of its neck vertical, and from the second position back to the first position, stopping the rotation of the bulb at the first position, permitting the excess lacquer to drain by gravity from the surface of the screen, removing the excess lacquer, drying the lacquer film by blowing relatively moist air within the bulb, and then drying the water under the lacquer film by blowing relatively dry air into the bulb.

15. The method of filming a wetted phosphor screen deposited on the surface of a plate-like support member, said member having an axis normal to the surface of said member at substantially the center of said member, comprising tilting said support member sothat said screen and the surface of said support member faces up wardly and said axis is positioned at an angle to the vertical, placing a quantity of liquid lacquer on a portion of said screen, rotating said support member slowly about said axis while simultaneously varying the angle of tilt of said axis at a slower angular rotation for causing the lacquer to flow substantially by gravity over the surface of said screen in a spiralwise motion to provide a coating on said screen.

16. The method of filming a wetted phosphor screen deposited on the concave surface of a support member, said support member having an axis normal to said concave surface of said member at substantially the center of said support member, comprising tilting said support member so that said concave surface of said support member faces upwardly and said axis is positioned at an angle to the vertical, placing a quantity of said fluid on a portion of said concave surface, rotating said support member slowly about said axis while simultaneously varying the angle of tilt of said axis at a slower angular rotation, the speed of rotation correlated with the angle of tilt to obtain an overlapping spiral coating of lacquer over the entire surface of said screen to provide a film over the entire surface of said screen,

17. The method of filming a wetted phosphor screen deposited on a surface of a plate-like support member, said support member having an axis normal to the surface of said support member and at substantially the center of said support member, comprising tilting said support member so that saidscreen and the surface of said support member face upwardly and said axis is at a first angle with respect to the vertical, placing a quantity of liquid lacquer on an edge portion of said screen, rotating said support member slowly about said axis while simultaneously reducing the angle of tilt of said axis at a slower angular rotation until the lacquer flows substantially by gravity over the entire surface of the screen in a spiralwise motion from the edge to the center region and then returning said axis to said first angle of tilt at substantially the .same speed while still rotating the support member about said axis to cause the lacquer to flow substantially by gravity over the surface of the screen in a spiralwise motion from the center region to the edge portion of said screen and eliminating the excess lacquer by gravity to provide a relatively uniform film of lacquer coating over said screen.

18. The method of filming a wetted phosphor screen deposited on a surface of a plate-like support member, said support member having an axis normal to the surface of said support member and at substantially the center of said support member, comprising tilting said support member so that said screen and the surface of said support member face upwardly and said axis is at a first angle with respect to the vertical, placing a quantity of liquid lacquer on an edge portion of said screen, rotating said support member slowly about said axis while slmultaneously reducing the angle of tilt of said axis at a slower angular rotation until the axis is sufficiently inclined vertioally to cause the lacquer to flow in an overlappingsplral path from the edge of said screen to the center region of said screen and then returning said axis to said first angle tilt of substantially the same speed while still rotating the support member about said axis to cause the lacquer to flow in an overlapping spinal path from the center region of the screen to the edge of the screen, stopping the rotation of the support member and permitting the excess lacquer to drain by gravity from the surface of the screen while said axis is at an angle with respect to the vertical.

19. The method of applying a uniform coating of hardenable fluid material upon a concave surface of a 1 support member, said support member having an axis normal to the surface of said member at substantially the center of said support member, comprising tilting said support member so that said concave surface of said support member faces upwardly and said axis is positioned at an angle to the vertical, placing a quantity of said fluid material on a portion of said concave surface, rotating said support member slowly about said axis while simultaneously varying the angle of tilt of said axis at slower angular rotation for causing the fluid material to flow substantially by gravity over the surface to be coated in a spiralwise motion to provide a coating on said concave surface.

20. The method of applying a uniform coating of hardenable fluid material upon a concave surface of a support member, said support member having an axis normal to said concave surface of said member at substantially the center of said support member, comprising tilting said support member so that said concave surface of said support member faces upwardly and said axis is positioned at an angle to the vertical, placing a quantity of said fluid on a portion of said concave surface, rotating said support member slowly about said axis while simultaneously varying the angle of tilt of said axis at a slower angular rotation, the speed of rotation correlated with the angle of tilt to obtain an overlapping spiral coating of fluid over the entire surface of said concave surface and eliminating the excess fluid by gravity whereby a relatively uniform film is provided over said concave surface.

21. The method of applying a uniform coating of a hardenable fluid material upon a plate-like member, said member having an axis normal to the surface thereof and substantially at the center of said member, comprising tilting said plate-like member so that the surface to be coated faces upwardly and said axis is positioned at an angle to the vertical, placing a quantity of said fluid material on a portion of said surface to be coated, rotating said plate-like member slowly about said axis while simultaneously varying the angle of tilt of said axis at a slower angular rotation for causing the fluid material to flow substantially by gravity over the surface to be coated without centrifugal force having appreciable effect on said fluid material.

References Cited in the file of this patent UNITED STATES PATENTS 1,806,920 See May 26, 1931 2,126,556 Hughes Aug. 9, 1938 2,642,365 De Gier June 16, 1953 2,644,770 Sadowsky July 7, 1953 2,726,167 Emmens Dec. 6, 1955 

1. THE METHOD OF FILMING A WATER WETTING PHOSPHOR SCREEN WITHIN A BULB OF A CATHODE RAY TUBE WITH LACQUER, SAID BULB HAVING A FACE PLATE AND A NECK PORTION, WHICH COMPRISES PLACING A QUANTITY OF LIQUID LACQUER WITHIN THE BULB, TILTING THE BULB SO THAT ITS FACEPLATE IS DOWNWARDS AND THE AXIS OF ITS NECK IS AT AN ANGLE TO THE VERTICAL, AND SLOWLY ROTATING THE BULB ABOUT THE AXIS OF ITS NECK AT A SPEED BELOW THAT AT WHICH THE CENTRIFUGAL FORCE WOULD HAVE AN APPRECIABLE EFFECT ON SAID LACQUER SO THAT THE LACQUER FLOWS IN A SPIRAL PATH OVER THE SURFACE OF THE SCREEN. 